A lot of water-based ink compositions which have erasability by an eraser has so far been proposed.
For example, disclosed in Japanese Patent Application Laid-Open No. 103997/2000 is an erasable ink composition in which a colorant contained in the ink is regulated around a certain size, that is, an erasable water-based ink composition comprising at least a colorant, wherein the above colorant has an average particle diameter of 2 μm or more, and the colorant having a particle diameter of 1.8 μm or less accounts for 1.6% by weight or less based on the colorant.
The ink composition described in the above gazette has erasability by an eraser, but it has the problems that the elimination of the colorant from a paper face only by light contact with the drawn lines so that the soiling of paper face is caused and that it does not stand actual use.
Further, disclosed in Japanese Patent Application Laid-Open No. 136339/2000 is an eraser-erasable water-based ink composition for a ballpoint pen provided with a point contact-like sticking property on the drawn lines after drying by blending particles having a glass transition point or a minimum film-forming temperature which exceeds 0° C. and is lower than 40° C. for the purpose of improving the performance of the drawn lines against abrasion. In the above ink composition, however, a film is sometimes formed depending on a temperature condition in writing, and therefore a problem resides in the points that the erasability is reduced and that starving in the beginning of writing due to film forming at a pen tip is caused, so that the eraser-erasable water-based ink composition for a ballpoint pen having stable quality is not obtained.
Further, disclosed in Japanese Patent Application Laid-Open No. 19888/2001 is an eraser-erasable water-based ink composition for a writing instrument having the purpose of improving the performance against abrasion by using adhesive colored resin particles provided with an adhesive property as a colorant. In the above water-based ink composition, however, a problem resides in the point that when writing is carried out after left standing for a certain time with the cap taken off, starving is liable to be caused, so that the good drawn lines can not be obtained.
Further, disclosed in Japanese Patent Application Laid-Open No. 19889/2001 is an eraser-erasable water-based ink composition for a writing instrument containing a colorant comprising colored thermoplastic resin particles and adhesive resin particles. The water-based ink composition using such a colorant has problems that it is liable to be instable with the passage of time and that erasability by an eraser is reduced when the drawn lines are left standing at a temperature of room temperature or higher for a certain period.
Further, in the water-based ink compositions described in the respective gazettes described above, it is not described that liquid media other than water are used. In the water-based ink compositions described in the respective gazettes described above, the colorants have to stay in the vicinity of a paper face in order to exhibit well erasability by an eraser. However, if a conventional scarcely volatile solvent blended in a lot of water-based ink compositions is used, the solvent penetrates into the inside of a paper face together with the colorant in a certain case without volatilizing, and therefore a problem resides in the point that using such a solvent is a cause by which the erasability is reduced. Accordingly, the current situation is that a water-based ink composition for a ballpoint pen which is excellent in erasability by an eraser is intensively desired to appear.
In light of the problems and the current situation of the conventional water-based ink compositions for a ballpoint pen described above having erasability by an eraser, the present invention intends to solve the above problems, and an object thereof is to provide a water-based ink composition for a ballpoint which is stable with the passage of time and which is excellent in a writing performance and erasability by an eraser.